Environment, Energy and Transportation Program
Invasive Species Web Report
15-Page Document
February 2001
Introduction
Exotic or invasive species are organisms-microorganisms, plants and animals-that have moved beyond their natural habitat and are competing with native species for food and territory. Invaders range from bacteria to vines to feral pigs. Invasions can be accidental or intentional, but the risk to native species is great in either instance. Exotic species compete with native species, alter habitats, change predator/prey relationships, and transmit foreign diseases or parasites. Exotic species also can cause a myriad of problems (food chain disruption, reduced biodiversity, clogging of water intakes, increased weed growth) and cannot be eliminated from a system without causing increased harm. Early detection and rapid response are essential to prevent major damage to ecosystems and the economy.
One reason it is so difficult to eliminate alien species after they are introduced into a new area is that there are no natural enemies to the alien invaders. Invasive species multiply rapidly, migrate quickly from area to area, and make themselves at home in a wide variety of conditions-at the expense of native plants, animals and, sometimes, native ecosystems. Invasive species, if left unchecked, can become the dominant species in large territories.
Invaders often go unnoticed until they have spread to many locations, making eradication difficult.
Effect on the United States
The spread of invasive plants, animals and pathogens is considered one of the most serious ecological problems facing the United States in the 21st century. Factors that contribute to invasive species are the great variety of climates and habitats in the United States as well as the large volume of international travel and trade. Ancient barriers-oceans, rivers, mountain ranges-have been breached. This makes the United States especially vulnerable to the introduction and establishment of invasive species. All regions of the country are affected by invasive species.
Invasive species have become an issue of state and national concern because of the adverse economic effects and long-term threats to the health and biological diversity of rural and urban areas. Invasive species cause huge losses in the agricultural, livestock and fisheries industries. Economic losses and expenditures resulting from the invasion or introduction of non-native species in the United States were estimated at $97 billion in 1991; current estimates are $138 billion a year.
Invasive species are estimated to infest more than 30 percent of the acreage of the National Park System in the lower 48 states. An estimated 6 million acres of the National Wildlife Refuge systems (38 percent of refuge lands in the lower 48 states) are affected by non-native plants. By a variety of estimates, invasive species contributed to the decline of 35 percent to 46 percent of the U.S. endangered and threatened species. Florida-where there are 23 known non-native fish species-spends more than $14 million a year just to control hydrilla, which was introduced into the state for use in aquariums.
Hawaii is the nation's capital of species extinction and endangerment. There, the threats of invasive species have reached crisis proportions. A growing number of highly invasive plants, amphibians, mammals, insects and wildlife diseases threaten an area that already has lost half its native birds and plants and 90 percent of its native land snails. Researchers have warned for years about the effect of wild pigs, goats, mongooses and other alien animals imported intentionally or accidentally.
How Exotic Species Are Introduced
Human activity usually plays a role in the introduction of an exotic species. Agencies that are responsible for safeguarding against alien introductions sometimes have themselves introduced the species. Exotic fish have been introduced to provide variety for sport fishermen or to boost the commercial fishing industry. In the past, the aquarium fish industry was the primary source of exotic fish; releases were both accidental and intentional. In other situations, one alien species may have been brought in to try to control or eradicate a previous invasive species, only to cause its own set of problems.
Two of the more recent methods of introduction of aquatic invasive species are aquaculture and the disposal of ballast water from cargo ships.
Aquaculture, according to the U.S. Department of Agriculture, is the " . . . manipulation of marine or freshwater organisms and/or their environment before eventual release, harvest or capture; the controlled cultivation and harvest of aquatic animals and plants." Two methods of farming fish and other aquatic species are to allow the free release of the species into regional waters or to contain the species in a circulation pen. A pen controls reproduction, food and growth, but changes to the environment cannot be controlled. If a non-native species is released in a regional area, the new species can affect the ecosystem by competing with or breeding with native species.
Ballast tanks on cargo ships are filled with water at foreign ports to help steady empty ships. Tanks then are emptied as cargo is loaded. Each tank holds millions of gallons of water that contain aquatic life-from bacteria and algae to worms and fish-native to the port where the tanks are filled. Ballast tanks are filled and emptied off the coastline and in estuaries and bays where freshwater and salt water meet. The exotic species picked up during filling can survive if they are emptied into conditions similar to their native habitat. As ships travel greater distances and world trade increases, species are introduced from across the globe. The United States receives 21 billion gallons of ballast water each year from around the world.
If ballast water were emptied into the ocean instead of into estuaries, rivers and lakes and the tanks were refilled with marine water, exotic species would be much less able to survive in a foreign location. The U.S. Coast Guard is responsible for implementing ballast water controls and initiatives. Currently, offshore ballast water exchange is mandatory in the Great Lakes and voluntary in Gulf, Atlantic and Pacific ports. The California Legislature approved legislation in 1999 that requires ballast exchange for ships enroute to its ports from the Pacific Ocean. (Cal. Fish and Game Code, §6430 et seq., 1999)
Since the early 1800s, exotic species have invaded or been introduced into the waters of the Great Lakes basin. Currently, about 159 non-native organisms are believed to live in the Great Lakes. In the majority of cases, introduction occurred as a result of human activities (shipping, canal building and deliberate releases). Several exotic species have had substantial effects on the Great Lakes. Aggressive fish-the sea lamprey, ruffe and round goby-attack native fish species such as trout, walleye, yellow perch and whitefish. The sea lamprey, in competition for food with Lake Michigan's lake trout, were responsible for the trout's disappearance. Lake trout now can be maintained only through stocking. Millions of dollars are required annually to manage, control and reverse the effects of non-indigenous aquatic nuisance species in the Great Lakes.
The Great Lakes are not the only United States waters to be flooded with foreign species. "Non-indigenous species are having a dramatic effect on marine, estuarine and fresh water ecosystems throughout the world," reported the Chesapeake Bay Commission in a 1995 report. More ship ballast water is dumped into Chesapeake Bay than anywhere else along the East Coast. Almost 90 percent of the ships entering Chesapeake ports carry live organisms in their ballast, according to the Smithsonian Environmental Research Center. In San Francisco Bay, an Asian clam is displacing native bivalves and eating the plankton that are an essential food source for a number of native species. A strain of cholera, discovered in Mobile, Ala., in 1991, resulted from ballast water release.
Economic and Environmental Effects
The effects of introducing an exotic species are both ecological and economic, and they are intertwined. An invasive species can have an economic as well as an environmental effect on its new home.
Invasive species displace native species by preying on the established food chain or competing with native plants for food or space. Without natural predators, invasive species can (and do) threaten or eliminate native species. Exotic species also carry the threat of new diseases that can destroy native inhabitants. In other instances, exotic species mate with native species, resulting in hybrids-changing the gene pool and simplifying the ecosystem, thereby causing a decline in population and reducing biodiversity. (Biodiversity is the variation and variety of genes, organisms and species found in an ecosystem.) If biodiversity decreases, the ecosystem is more vulnerable to pests and diseases.
Changes to ecosystems and biodiversity as a result of an invasive species can result in fires, floods and erosions. In the intermountain West, invasive plants--such as cheatgrass--are replacing native species, increasing the frequency and intensity of grass fires and damaging the value of rangeland. Alien invaders have taken over a third of the 75 million acres of the Great Basin in California, Idaho, Nevada, Oregon and Utah. Grazing and fire are two important factors in the western United States that allow exotic plants to invade. Foreign species of weeds drove out sagebrush and fueled the most catastrophic fire season in the last 50 years. The habitat change also is affecting the sage grouse and big game.
Recent U.S. Geological Survey studies show that non-native annual grasses dominate most plant communities in the Mojave Desert in eastern California. These grasses are able to grow in many different situations and create continuous fuel beds across the desert landscape, allowing fires to spread and attack native perennials. Dried non-native grasses stay rooted in dense stands that ignite easily and carry fire rapidly across a large area. Non-native annual grasses also dominate areas after a fire. The wildlife that survive a fire can be adversely affected by the changing plants in their habitat.
Aquatic invaders-the zebra mussel, the Asian clam, giant salvinia and purple loosestrife-are transforming wetlands and inland waters and reducing their value for wildlife and recreation.
Economic sectors affected by invasive species are agriculture, forestry, fisheries and water use, utilities, and natural areas. Exotic species cause economic damage by 1) hybridizing with valuable species to produce worthless hybrids; 2) carrying or supporting harmful pests; 3) reducing recreational prospects in an area; 4) affecting the social and health consequences of the area. The United States spends hundreds of millions to billions of dollars trying the repair the damage caused by harmful exotic species.
Exotic species affect not only native species but also can affect people. Cures can be costly. The exotic species may be poisonous, be a vector (carrier) for human disease, or create conditions for disease to spread. A few invasive species-such as the West Nile virus-are carriers of human diseases. Hybrids of native and exotic species may be dangerous or poisonous and humans may consume them without knowing the danger.
Policy Options
An effective, coordinated response is needed to reduce the effects of invasive species. The following examples demonstrate measures that state and federal governments are taking to combat specific invasive species and their effect on native species. Adoption by regulators of a precautionary approach that has realistic goals, incorporates scientific information and provides opportunities for those developing aquaculture enterprises will benefit everyone.
(Case study summaries of specific invasive species are included in the Appendix on page 20.)
Zebra Mussels
Eurasian zebra mussels first were identified in Lake St. Clair near Detroit, Michigan, in 1988. By 1990, they were found in all the Great Lakes. The mussels have spread throughout the Great Lakes, across the eastern United States and down the Illinois, Mississippi and Hudson rivers to establish strongholds in 20 states.
Because no environmentally safe method exists to control zebra mussels, the best method of controlling this species is through public awareness and education. Environmental agencies and other organizations suggest boaters remove attached vegetation and wash boats and trailers before moving them to new lakes and rivers; flush engine cooling systems, bilge areas and live wells with tap water; leave unused bait and bait bucket water behind; and inspect boat hulls for signs of tiny hitchhikers. Texas and Florida have established check points where officials look for zebra mussels attached to boats.
"Make sure your boat is clean and you're not bringing or transporting any plants or moving water between different water bodies in the state, particularly ones that you know have zebra mussels."
Senator Ken Sikkema (Mich.), chair of the Senate Natural Resources and Environmental Affairs Committee, has proposed legislation (S.B. 955) to keep the zebra mussel and other invasive species such as the sea lamprey, ruffe and round goby out of the Great Lakes. The bill requires oceangoing freighters to treat ballast water to kill foreign species before the water is dumped into the Great Lakes. The bill directs the state Department of Environmental Quality to develop a rule addressing the treatment of ballast water. Ships that remain within the Great Lakes Basin would have to adopt "best management practices" to eliminate any species they might have picked up in ballast water. These practices could include regular rinsing and inspections of screens to check for foreign species.
"It's the most serious problem facing the lakes and it's actually getting worse," says Sikkema, who cites figures indicating that the number of non-native species has grown from 139 a decade ago to 159 currently. "My goal is to effectively protect the Great Lakes from any new introduction of non-native species. It's easier and more effective to do that if you have one law at the national level with a similar law in Canada that is strong and effective and does the job . . . but that's not going to happen until individual states start getting laws passed and demonstrating that they're serious about this problem." If a federal or international program was adopted to address the problem, the Michigan law could be suspended.
Governor John Engler (Mich.) and his staff prefer a regional approach to addressing non-native species, rather than individual state laws. "You need a basin-wide solution, " according to Russ Harding, director of the Michigan Department of Environmental Quality. There is no indication at present that a regional agreement or federal law is imminent, despite the introduction of ballast water legislation (H.R. 4191-Hoekstra, Mich.) during the 106th session of Congress.
The Illinois Natural History Survey, a division of the Illinois Department of Natural Resources, is working with municipal, state and federal entities to design an experimental barrier to curtail the downstream movements of invasive species from Lake Michigan into the Illinois River (and vice versa). The U.S. Army Corps of Engineers is to install the first phase of the electrical barrier in summer 2000 at the Chicago Ship and Sanitary Canal. The barrier will physically isolate fish in the Great Lakes from fish in the Mississippi River Basin and the canal by closing an opening between the two watersheds. INHS researchers at the Lake Michigan Biological Station will study the ability of fish to move across the barrier, providing insight into the feasibility of barriers as deterrents to the spread of exotic species.
A survey of Illinois boaters and anglers to determine their knowledge of and attitudes about exotic species indicated that this group lacked information about the potential spread of exotic species via fishing and boating activities and equipment. Funding from the Illinois-Indiana Sea Grant College Program and the EPA's Great Lakes National Program Office is being used to support outreach projects targeted at boaters and fishermen. Large metal "Exotic Species Advisory" signs have been produced and placed at boat landings along Lake Michigan's Illinois shoreline. These signs caution boaters about the potential effects of exotic species and encourage boaters to take the necessary steps (washing the boat before traveling to another waterway) to prevent accidental spread of these species. A brochure about exotic species and steps to preventing their spread also has been distributed. Displays in bait shops assist fishermen to identify the round goby; stickers for bait buckets remind anglers not release unused bait into a lake or river.
The University of Minnesota Sea Grant Program has produced and distributed an 11-minute clean boating video to educate boaters about the best ways to prevent the accidental spread of alien plants and animals. "If boaters are given information about exotic species and how to prevent their spread, they'll do something about it," says Marie Zhuikov, communications coordinator at the University of Minnesota Sea Grant Program. The video includes five steps boat owners should take when moving their personal watercraft, motorboats or sailboats from one water body to another. Footage from across the United States is used and three exotic species are profiled during the video. More than 6,500 copies of the video have been distributed nationwide, and several agencies have developed public service announcements from the footage.
Pierce's disease and the glassy-winged sharpshooter
The glassy-winged sharpshooter is a serious new pest in California. Although the insect is native to the southeastern United States, it was first observed in California in 1990. The sharpshooter threatens California vineyards because it is the carrier for Xylella fastidiosa, the baterium that causes Pierce's disease, which kills grapevines and for which no effective treatment exists.
The California Legislature approved S.B. 671 (Chesbro), and Governor Gray Davis signed the bill into law on May 19, 2000. The bill appropriates $6.9 million to the Pierce's Disease Management Account within the state Department of Food and Agriculture to be used to combat Pierce's disease and its vectors before the disease and the glassy-winged sharpshooter can destroy the grape industry. A bill approved by the Legislature in 1999 (A.B. 1232, Cardoza) established a grants program, administered by the Department of Food and Agriculture, to fund research into Pierce's disease and its vectors. The wine industry provides a 25 percent match to state funds, and $1 million per year is available for three years. An advisory task force recommends suitable projects for grant funding.
The overall program goal is to reduce the economic effects of the glassy-winged sharpshooter on the state's grape, almond, peach, citrus and nectarine industries through a coordinated state and local plan. The first steps include a statewide survey to determine the current distribution of the glassy-winged sharpshooter, followed by inspection of nursery stock and other commodities that could carry the insect. The state will develop and share information about the nature, characteristics and effect of the insect on various crops as well as on the economy and quality of life. The state will provide 1) training in biology, detection and treatments of the disease and its carriers, and 2) establish treatment protocols for rapid response to eradicate or manage infestations.
Nutria
Nutria is a semi-aquatic rodent that loves wetland vegetation. Efforts have focused on increasing the economic value of nutria to encourage harvesting. Louisiana provides incentives to trappers and meat processors by creating a fur marketing cooperative to increase the profitability of pelts. (La. Rev. Stat. Ann. § 281 et seq., West 1999) The state attempts to market nutria meat as an inexpensive source of protein. The Barrataria-Terrebonne National Estuary Program is exploring marketing opportunities around the world for nutria meat and pelts. None of these efforts have significantly decreased the nutria population. Louisiana received $2 million in federal funding in 1998 to control the nutria.
Trapping has been the primary control method, but efforts have not been successful. Trappers on a private site in Dorchester County, Maryland, harvest more than 4,000 nutria per year. Despite these efforts, the nutria population remains between 13,000 and 20,000 animals. The only other known control for their further expansion is cold weather.
Understanding the nutria's reproductive behavior may be key to controlling this invader. In Maryland, a state, federal and nongovernmental team of biologists and natural resource managers have been collaborating for 10 years as the Marsh Restoration and Nutria Control Partnership. The team devised a three-year nutria control program. The partnership is attempting to control nutria populations, although eradication still may be possible. Isolated attempts to control nutria are not effective; a comprehensive approach is necessary. The partnership is seeking funding for its $2.9 million program. The U.S. Fish and Wildlife Service, U.S. Department of Agriculture (USDA) and the National Fish and Wildlife Foundation have committed more than $800,000 to launch a pilot program.
The partnership has hired 12 trappers to remove nutria from project test sites. Two graduate students will research the demographic and reproductive responses to intensive harvesting in conjunction with the University of Maryland's Eastern Shore campus. The students are trapping 2,000 nutria to serve as a baseline for biological data. Once the selected sties have been cleared of nutria, a team of scientists will conduct experiments about how the nutria move through wetlands. The program also will include public education about the damage caused by nutria on both the natural and economic systems of the region. The state does not want to encourage market incentives as a control measure because this would give the rodents a tangible value that could make future eradication socially unacceptable. If extermination is not successful, control of the population to a manageable level and market incentives may be other options.
Yellow perch and Rotenone
Yellow perch have invaded Alaskan lakes to the detriment of native sportfish and commercial salmon fisheries. Prolific breeders, perch are well suited to cold, northern lakes. If perch gain access to a river system such as the Kenai, Swanson or Kasilof, they dine on juvenile salmon and fish eggs. It is illegal to stock non-native fish in Alaska, but no one has ever been charged with the crime because it is so difficult to catch anyone in the act. The Department of Fish and Game is promoting stricter penalties to deter would-be amateur fish stockers.
The Department of Fish and Game is testing whether the pesticide rotenone can be used to kill non-native perch. Minnesota uses rotenone in its lakes to kill black bullhead and carp in order to restock walleye. The pesticide, an organic pesticide that is a derivative of South American plants, affects fish an makes it impossible for them to process oxygen. The pesticide breaks down rapidly and a lake can be restocked with fish in two to three weeks. Rotenone poses little risk to humans, and the dead fish can be eaten safely by mammals and predatory birds. (Note: Dr. Timothy Greenamyre of Emory University reports in an article in Nature Neuroscience that rotenone could contribute to Parkinson's disease in humans.) The state will gauge public opinion before treating other lakes infested with pike and other non-native species.
Kudzu
Kudzu is a woody vine that is a member of the legume (bean) family. David Orr, an entomologist at North Carolina State University, is attempting to identify a biocontrol for kudzu. Orr, in collaboration with Chinese scientists, is studying a large beetle that eats kudzu roots. The beetle has not been imported to the United States because of concern that the beetle also will eat soybeans, a cousin of kudzu. In China, humans are kudzu's worst enemy. People use kudzu vines to make rope and dig the roots to use as a hangover remedy.
In a state-supported program, the city of Tallahassee, Florida, is attempting to use 300 sheep and a shepherd to control several hundred acres of kudzu that covers public parklands in the capital. The five-year program ( begun in spring 2000) is based on a proposal by Bellwether Solutions, a New Hampshire company that uses sheep to control weeds in other locations. "The sheep are loving the kudzu. This could be a way for small farmers to fatten up their animals with free food and at the same time eradicate a pest plant," says Larry Schenk, Tallahassee parks superintendent.
The herbicide Transline works fairly well on kudzu, but a single gallon of concentrate costs $300 and treatment requires several applications over a number of years to eradicate one acre. Transline is banned throughout Florida because it is a groundwater pollutant. Mowing a kudzu plot for four or five years-if the land isn't too rough and the vines aren't too thick-will kill it. Digging the roots also works, but a 20-year-old plant that has never been cut back can have a single root weighing 250 pounds; a backhoe is required to dig it out. John Byrd, a professor of weed science at Mississippi State University, has begun a five-year test of various herbicides to test their effectiveness on kudzu.
The Illinois Department of Natural Resources, along with the U.S. Fish and Wildlife Service, the Natural Resources Conservation Service, the state Department of Transportation, Shawnee National Forest and two state universities, are developing plans to begin a cooperative kudzu eradication program. All agencies except the U.S. Forest Service treat kudzu populations on their properties with a legume-specific herbicide. (The Forest Service does not permit the use of herbicides to control exotic plants.) Results of the herbicide treatment have been positive. Populations that were an acre in size in 1998 did not grow additional vines in 1999.
Due to the large, starchy roots, kudzu can remain dormant in the soil for many years; continued surveillance will be necessary to ensure that kudzu is eradicated in Illinois. Plans are under way in Illinois for a statewide eradication program on both public and private lands. If successful, Illinois will be the first state to undertake and complete a kudzu eradication program.
Cheatgrass
Cheatgrass is a native of the steppes of Central Asia. Bureau of Land Management (BLM) and U.S. Department of Agriculture (USDA) scientists are urging replanting native grasses such as bitterbrush and bunch grass for the elk to graze on. Reseeding after fires is standard practice to prevent erosion, but often native grasses are not used. "To really restore those sites is going to require reintroduction of seeds, trying to remove the weeds to reduce competition and then reestablish the native species," says Steve Monsen, a USDA botanist.
USDA's Rocky Mountain Research Laboratory and Shrub Sciences Laboratory, as well as their counterparts with the BLM and state and federal biologists and rangers, are fighting the weeds that are uprooting native plants. The BLM has announced its Great Basin Restoration Initiative, a plan to replant 500,000 acres, some with native species at a cost of $10 million per year for at least 10 years. In comparison, BLM now spends $71 per acre per year to put out fires, plus $64per acre for rehabilitation after fires and $70 per acre in weed control. BLM is seeking $2.5 million in FY 2001 funds.
Congressional Action
Congress passed the Nonindigenous Aquatic Nuisance Prevention and Control Act in 1990. In 1996, a companion bill, the National Invasive Species Act, was passed; it included a ballast water management program. Despite these federal measures, United States' oceans, lakes, rivers and estuaries still are plagued by invasive species that cost states and taxpayers billions of dollars each year.
Executive Order and Federal Agency Action
In his Executive Order on Invasive Species (No. 13112) issued in February 1999, President Bill Clinton directed federal agencies to develop, coordinate and carry out efforts to prevent and control this growing threat. The executive order established a cabinet-level Invasive Species Council, responsible for identifying, eradicating restoring and eliminating potential pathways for aquatic species introductions. A national invasive species management plan is being prepared. Five regional management areas-the Great Lakes, West Coast, Gulf of Mexico, Southeast and Northeast regions-were established in the order. Each region has a panel of state representatives.
The U.S. Fish and Wildlife Service reports that battling invasive species is one of its highest priorities.
The United States as an Exporter of Exotic Species
The United States also exports exotic species. The American comb-jelly arrived in the Black and Azov seas in Europe from the United States via ballast water. The comb-jelly, a small, marine invertebrate that resembles a jellyfish, is carnivorous and preys on tiny aquatic animals such as plankton. The plankton in these areas have been reduced by as much as 90 percent, resulting in a decrease in the anchovies that feed on plankton and adversely affecting local fisheries.
Appendix
Case Studies of Specific Invasive Species
Zebra mussels and other aquatic invasive species
Eurasian zebra mussels first were identified in Lake St. Clair near Detroit, Michigan, in 1988. By 1990, they were in all of the Great Lakes. The mussels have spread throughout the Great Lakes, across the eastern United States and down the Illinois, Mississippi and Hudson rivers to establish strongholds in 20 states. Zebra mussels expand their range by several methods-larva float downstream or are carried in containers such as bait buckets; adults attach themselves to boats and other hard surfaces.
The zebra mussel has generated more than $3.1 billion in damages in 10 years to intake pipes, water filtration equipment and electric generating plants. In addition to clogging pipes, the mussels reproduce rapidly and displace native freshwater mussels. Each mussel lays more than 40,000 eggs in one reproductive cycle and up to 1 million eggs in a spawning season. Zebra mussel densities were as high as 700,000 per square yard at one Michigan power plant. Already declining native mussel populations of the Mississippi River system could be reduced by as much as 50 percent in 10 years by zebra mussel invasions. Zebra mussels cost the United States $5 billion in control efforts and reparation.
Many species first introduced into the Great Lakes have been transferred to inland lakes, rivers and streams both near to and far from the region. In addition to boating and fishing, the Chicago-area canals built to reverse the flow of the Chicago River have enabled the round goby (a fish species) and the zebra mussel to move downstream from Lake Michigan into the Illinois and Mississippi rivers.
Six lakes in the greater Chicago area have been confirmed with zebra mussel infestations; most likely they were introduced into the lakes on boats or boat trailers previously used in infested waters (Lake Michigan). Minnesota recently reported that zebra mussels have been discovered in Zumbro Lake, north of Rochester. Zebra mussels have been living in the Duluth-Superior harbor and the Mississippi and St. Croix rivers, but this is the first report of their discovery in a Minnesota inland lake. Southeastern Wisconsin reports a dozen lakes with zebra mussels and Michigan has about 100 infested lakes. Zebra mussels also have been found in the Missouri River south of Sioux City, Iowa. The round goby has been introduced from the Great Lakes into two inland rivers in Michigan, most likely by fishermen using them as bait.
The zebra mussel population continues to grow and there is no immediate end foreseen to this invasive species. The only known predator is the round goby, another rapidly-spreading European invader that creates as many problems as it solves.
Another Great Lakes invader, the fishhook flea, is a tiny zooplankton stowaway in ballast water from Eurasia. This predatory crustacean was first discovered in Lake Ontario in 1998, and was found in plankton samples in Lake Michigan in 1999. It is not known what effect this new species will have on the Great Lakes ecosystem. The flea eats other species of zooplankton that are the primary food for many fish species. Although fish species may eat the flea, scientists are not sure it provides them any nutritional value. The flea has a long, spiny appendage that clogs reels and fouls fishing lines and nets in the Great Lakes.
The fishhook flea is transported in water from lake to lake. Control measures include emptying, washing and drying gear, recreational equipment and bait buckets. The dormant eggs, unfortunately, can hatch after they have dried or been frozen, even several years later.
The grass carp is a native of Russia and China. This aquatic plant eater consumes two to three times its weight each day and can gain 5 to 10 pounds each year. Grass carp is a popular sport fish that can grow to 3 feet in length and weigh up to 100 pounds. Grass carp were introduced into Lake Conroe in Texas in the 1980s as a control for hydrilla, an invasive plant. The carp migrated from the lake and into the Trinity and San Jacinto rivers. After the carp cleaned the hydrilla from Lake Conroe, the fish began eating grass from waterfront property and leaves from low-hanging branches.
Texas has built enclosures around specific areas of Lake Conroe, and carp are selectively released into these areas to eat vegetation. Once that section of the lake is cleared, the carp are moved to another portion of the lake.
Nutria, a semi-aquatic rodent, loves wetlands vegetation. These South American transplants, introduced to the United States in 1937 as an effort to spur the fur industry, have established themselves in 14 states from Oregon to Maryland and are destroying wetlands as they spread. The speculative trade in nutria fur proved unprofitable and many nutria farms went out of business. The animals escaped or inadvertently were released from the farms. The population has grown from 13 original animals to a Gulf population of 5 million. Nutria chew on the roots of salt marsh plants, sugar cane and rice, causing coastal erosion. Nutria paths and nesting areas create depressions and channels within the wetlands; the dying plants allow open water and the channels act as conduits to transport sediments out of the marsh system. Damage to seagrass beds along the Chesapeake Bay affects the Tangier Sound blue crab fishery. Nutria also have had a negative effect on muskrat populations and the trapping of these furbearing animals. Nutria and muskrats compete for food, nutria activities reduce muskrat habitat, and nutria destroy muskrat lodges to create their own nesting areas.
Nutria are extremely fertile, reproducing as often as three times per year; the average litter is five, but litters of 13 have been noted. In Maryland, 65 percent of all adult females are pregnant at any given time. In Louisiana, nutria populations have grown so large that most biologists agree that eradication is impossible.
Researchers in the United States note that the United Kingdom eliminated its nutria population, but only after 10 years. Research indicates that nutria populations are density dependent and that harvesting nutria at the wrong time of year actually may induce the animals to increase reproduction.
The glassy-winged sharpshooter and Pierce's Disease
The glassy-winged sharpshooter is a serious new pest in California. In the Temecula Valley, 200 acres of grapes have been destroyed and another 300 acres have been damaged and most likely will be dead within the next two years. Grape production is a $2.4 billion industry in California and the wine grape industry contributes $32.7 billion to the state economy.
Other crops that could be affected are almonds, citrus, nectarines and peaches. The bacterium, the source of almond leaf scorch, alfalfa dwarf, oleander leaf scorch and citrus variegated chlorosis (citrus X), could be a threat to a number of agricultural producers throughout California. Citrus X disease has caused significant damage to the citrus industry in Brazil.
The insect is abundant in areas with diverse summer and winter hosts. The sharpshooter feeds on a variety of ornamental, native and crop plants. In southern coastal areas, the insect prefers to winter on oleanders and deciduous fruit trees such as peaches and apricots. Bacterial leaf scorch, also caused by X. fastidiosa, is killing pin oak, red oak, maple, sycamore and sweet gum trees in Kentucky. The bacterium is found from Long Island to Florida and along the Gulf Coast. In Washington, D.C., the scorch is destroying elm and oak trees along the National Mall.
The glassy-winged sharpshooter feeds on stems and leaves. When large numbers of glassy-winged sharpshooters feed on a plant, white residue can be seen on the leaves, oozing sap (sharpshooter rain) onto foliage and sidewalks. The X. fastidiosa bacterium deposited by the sharpshooter blocks tree arteries and causes them to die of thirst. The bacteria builds up in the xylem, the tissue that carries water in trees and grapevines. The insect attacks citrus plants by feeding on the leaves and depositing its eggs in the rind of the fruit, making it unmarketable.
The first sign of infection in trees is brown tips on leaves; the disease is slow growing and does not attract much attention. However, early detection is important for developing control strategies. Yellow sticky traps hanging in orchards and vineyards are useful for monitoring the sharpshooter. Plants can be examined either by direct examination or by use of a sweep net. The only treatment for infected deciduous trees is an injected antibiotic, but the injections can eventually kill the tree. Removing and replacing dying trees will cost homeowners and local governments hundreds of thousands of dollars.
Asian longhorned beetle
The first Illinois infestation of the Asian longhorned beetle was discovered in the Ravenswood neighborhood of Chicago in July 1998. Smaller infestations soon were detected in DuPage County and southern Cook County. The beetle could attack the 90,000 acres of Forest Preserve Districts in Cook and DuPage counties (Ill.), as well as the 500,000 trees lining the streets of Chicago. More than 11 percent of Cook County is a forest preserve, and the majority of trees are acceptable hosts for the Asian longhorned beetle. The beetle attacks hardwood trees, eventually killing them. Some 50 percent of Chicago's trees are maples, one of the beetle's favorite foods; overall, 70 percent of the city's trees are susceptible. The telltale signs of infestation are dime-sized adult exit holes or the egg-laying sites high in the tree canopies. Early detection of infestation and rapid treatment are crucial to successful eradication. Bucket trucks and tree climbers from the U.S. Forest Services' smoke jumpers corps have been used to identify infested trees.
Because the larva live deep inside infested trees during most of the year, conventional insecticide sprays are not an option. Removal and destruction of infested trees currently is the best tool available to eliminate and control the Asian longhorned beetle. Tree-cutting operations began in the Ravenswood community in February 1999; 837 tress were felled, chipped and burned. An additional 314 infested trees were discovered during additional survey efforts. The infestations in DuPage and southern Cook counties resulted in the loss of another 78 trees.
Selecting trees for replanting focused on tree species thought to be resistant to beetle attacks (oaks, lindens, gingkos, tulip trees, and the honey locusts). City foresters began replanting operations during summer 1999.
Because the Asian longhorned beetle is not a particularly strong flier, it does not appear to be rapidly expanding its range. Several new spot infestations have been found outside the quarantine boundaries. Intensive survey and tree removal will likely continue for five or more years at a cost of several million dollars to the city before it can be determined whether the eradication attempts have been successful.
Soybean aphid
An exotic Chinese aphid, Aphis glycines, has infested soybean fields in Illinois, Michigan and Wisconsin. Scientists in these states are trying to learn more about the aphids, which ravage soybeans in China. They were first found in the United States in July 2000 by Wisconsin researchers. Researchers and farmers found soybean plants covered with aphids in Wisconsin, southern and northern Illinois, southern Michigan, Minnesota, Ohio and Indiana. The aphid infestations cause the soybean leaves to yellow and cup.
The aphid can multiply quickly and survive harsh weather. The aphid can winter on the buckthorn, a woody shrub that also is an invasive species. The damage to the 2000 crop appears limited, but there is concern that the pest will spread quickly and pose a threat to future crops. Scientists are unsure how the pest was introduced into the United States. Common pesticides are not labeled for treating the aphid because they are too new to the country. Some treatments are being tested in the laboratory to determine what might work. Most of the scientific literature is written in Chinese. Kevin Steffey, a University of Illinois entomologist, says, "A lot of entomologists and plant pathologists are planning to learn as much as we can about the soybean aphid before the 2001 growing season. We want to be prepared for whatever it may bring next year."
Ladybugs, strong rains and fungus kept the aphids at bay in sections of Illinois during summer 2000. The ladybugs ate the aphids; the insects also succumbed to driving rains that washed them off the leaves and to a fungus that proved toxic to the aphids but not to the beans.
West Nile virus
The West Nile virus first came to light in 1999 in New York City where seven older people died of encephalitis (an inflammation of the brain). This virus has been found in birds-especially crows and robins-in Connecticut. The virus being spread throughout the northeast United States by an infected bird population. Crows are particularly susceptible to the virus and are good indicators of the virus' presence. The virus is passed to humans through mosquito bites. No one is sure how the virus entered the United States.
New York City sprayed the pesticide malathion in fall 1999 to battle the West Nile virus. Opponents to malathion believe the pesticide poses a greater threat than the virus. New York City now is using two other pesticides, Anvil and Scourge, that are similar to a natural substance produced by chrysanthemum flowers that is toxic to mosquitoes.
Other viruses
Four shrimp viruses found in the Gulf of Mexico have been shown to infect the commercially valuable brown, pink and white shrimp species. Domestic harvest produces 200 million pounds of shrimp annually; domestic aquaculture produces less than 1 percent of U.S. consumption. The major potential pathways of virus infections include shrimp processing plant wastes and waste products and migrate from aquaculture ponds. Other sources include infected bait shrimp, ship ballast water, research and display facilities, fishing vessels and birds that naturally spread the virus. Management options for control are under study.
Algal blooms and red tide are carrying toxins into previously unharmed waters. There are more than 60 harmful algal toxins today, compared with 22 in 1984. Blooms grow over vast areas of surface water, blocking sunlight and air exchange. When the blooms die, the plants sink to the bottom of the ocean and consume more oxygen. Eventually, so much oxygen is depleted that fish begin to die. In the Gulf of Mexico, 9,600 square miles of water were rendered biologically dead in 1997. Harmful algal blooms are associated with fish and invertebrate kills and disease, bird and reptile losses, seafood poisoning and human respiratory problems. An estimated $1 billion in economic loss has been attributed to algal blooms during the past 10 years. Red tide also was implicated in the manatee die-off in southwest Florida in 1996. Researchers are using satellite sensing devices to predict and track algal blooms. Coastal areas act as a natural filter that can slow down incidences of algal blooms.
Kudzu and other plant invasive species
Kudzu is a woody vine that is a member of the legume (bean) family. The seeds can remain in the soil for several years before germinating. The vines develop from starchy tubers that can grow to depths of 10 feet and weight 200 pounds to 300 pounds. Kudzu can root at the leaf joints, forming thousands of plants to the acre. Kudzu has an amazing growth rate of up to 1 foot per day and 60 feet per year.
Kudzu, a native to East Asia, has been used for centuries to make tea, health tonics and kimono fibers. Kudzu was brought to the United States as an ornamental vine to shade the Japanese pavilion at the 1876 Centennial Exposition in Philadelphia. Around 1900, a Florida farmer threw some Japanese vines onto his trash pile. The vines rooted and covered the pile and adjacent land. The farm animals (cows, chickens, goats and pigs) liked the vines and its fragrant flowers. In those early years, kudzu was used as a control for soil erosion, and the leaves were used as fodder for livestock, the vines for basket-making and the tuber as a thickening agent for foods. The U.S. Soil Conservation Service began testing kudzu in 1935, believing that the plant-with its fast growth and deep roots-could solve the South's erosion problems. Farmers were paid $8 an acre to plant kudzu on eroded lands. The Soil Conservation Service shipped 100 million plants in the 1930s and 1940s from nurseries in Georgia and Alabama. The Civilian Conservation Corps planted more than 70 million seedlings from Maryland to Texas during the 1930s. Some individuals became concerned, however, about the rapid growth of the plant. Kudzu refused to stay put; it invaded valuable crop land, infested forests, climbed utility poles, and damaged telephone and power lines. Farmhouses where kudzu originally was used for porch shade were overrun.
In 1953, the U.S. Department of Agriculture removed kudzu from its list of acceptable cover crops. Research shifted from establishing kudzu to methods of eradication. Eradication kudzu has not been as successful as promoting its use. By the 1980s, kudzu covered an estimated 7 million acres of land in the southern United States-an area roughly the size of Massachusetts. Each year, the amount increases by another 320,000 acres. Kudzu is most abundant in Alabama, Mississippi, Georgia, North Carolina and South Carolina. Today, kudzu is spread mainly through human activity like construction and road building, both of which are growth industries in many areas in the South. "All you need is one root in a truckload of fill and you have a new kudzu infestation," says David Orr of North Carolina State University.
Kudzu has been moving north, finding the climate friendly in Connecticut, Delaware, Illinois, Massachusetts, New York and Pennsylvania. A sand dune at Shoreham, Long Island, New York, is covered with kudzu. Kudzu colonies in southern Illinois range in size from less than 1 acre to 40 acres.
Cheatgrass is a native of the steppes of Central Asia. It arrived in the Western United States in 1910, most likely with imported grains planted on the range. Cattle and sheep grazed the land for decades, stripping away the sagebrush and native grasses and allowing the cheatgrass to take hold and spread. Cheatgrass is a winter annual-its seeds germinate in early fall and through the winter in warm areas so it has a head start on other plants in early spring. Spring annuals such as sagebrush cannot compete with cheatgrass that already has grown to full size, dropped seeds and died. Dry cheatgrass provides tinder for summer lightning, campfires or sparks from a car. With dead grass as a fuel, fires burn hotter and spread faster, setting up a vicious cycle. Fires clear acres of native brush, making the area susceptible to cheatgrass (its seeds are flame-resistant) and allowing it to spread even farther.
Purple loosestrife was first introduced to New England and New York City from Europe in the early 1800s and was used in gardens and landscaping projects. The European insects that fed on the plant and controlled its growth were not imported along with the plant. This plant now is found throughout the United States, where it destroys marshes; chokes waterways; and threatens native species, wildlife, butterflies and amphibians that rely on wetlands for food and shelter. The distribution and importation of purple loosestrife is banned in 24 states, and more than $45 million is spent annually to control its spread.
At the Columbia Basin Project in Washington, the federal government is attempting to use beetles to biologically control and combat purple loosestrife. The leaf-eating beetles feast on the purple loosestrife and, in turn, keep irrigation channels flowing so farmers can water crops. The Winchester Wasteway returns irrigation water to allow its reuse to irrigate other acres. In the early 1960s, a university experiment introduced purple loosestrife to the area. The aggressive invasive species soon spread to almost 20,000 acres. A perennial, non-native plant with purple flower spikes, the species is deadly for wetlands across the United States. It crowds out desirable wetlands plants and reproduces in large numbers-one plant can produce several million seeds per year.
In the past, herbicidal control was attempted to control purple loosestrife on a limited basis, but the monetary and environmental costs to repeatedly spray a large area were prohibitive. Biological control-using insects to eat the plant-seems to be working. The Washington state project began in 1995 and today, 2,500 acres of purple loosestrife either has been reduced to bare stems or damaged so that the plants cannot flower and reproduce. Beetles have been transplanted to other parts of Washington and Idaho to control purple loosestrife.
Canada thistle is a noxious weed that reduces crop yields. The weed is so invasive that officials say it will surpass leafy spurge (a pesky weed that has been a problem for many years) in total acreage by 2002. Canada thistle spreads more readily in cropland, while leafy spurge thrives on rangeland. Canada thistle infests more than 900,000 acres and the amount increases by nearly 100,000 acres per year. Because it is a perennial, the entire plant must be killed to prevent regrowth from rootstock. Canada thistle is native to Eurasia and probably was introduced accidentally in the early 17th century. One of the most widespread, tenacious and economically damaging weeds in the United States and Canada, it has been declared a noxious week in nearly every state..
Leafy spurge, an invasive plant from Eurasia, causes more than $100 million in damage annually in the Great Plains states. Much of the damage is to livestock producers. Researchers are studying control practices such as use of herbicides and biological controls with flea beetles.
Hydrilla, a native of Asia, Africa and Australia, is an aquatic plant that was introduced in Florida in the 1950s as an aquarium plant. Hydrilla has spread throughout the southern United States and as far north as Washington. Hydrilla forms thick, green carpets across the surface of the water, makes waterways impassable and shades out most of the vegetation below. Hydrilla can grow at a rate of 10 inches per day and spread from a few acres to several thousand acres in a short period of time. In an attempt to contain hydrilla, Florida spent more than $50 million in the 1980s.
Rivers and lakes need to be inspected often so that control efforts can begin early. Once established, hydrilla is nearly impossible to eliminate. Lake Jacksonville, Texas, was able to eliminate hydrilla through an integrated approach. Hydrilla biomass was reduced with an aquatic herbicide, a small school of grass carp was stocked to control resprouting and a diverse native plant community was reintroduced.
The water hyacinth, a South American native introduced to New Orleans, Louisiana during the World Industrial and Cotton Centennial Expo in 1884, once was a popular ornamental plant in the United States. The water hyacinth grows rapidly and forms dense, floating mats in rivers, lakes and waterways. The mats prevent sunlight from reaching underwater vegetation and crowd out native plants; this increases the deposit of organic matter into the water and destroys the oxygen below the surface. Water hyacinths can double in size in six to 18 days. This rapid growth frustrated homeowners and landscapers, who threw excess flowers into nearby waterways. Florida spends $11 million each year just to manage water hyacinth. The hyacinth can be controlled by aquatic pesticides and natural plant-eating predators.
Melaleuca and other invasive species in the Everglades
In the Everglades National Park (Fla.), several invasive species are attacking. Melaleuca, is an ornamental Australian tree. It forms impenetrable stands that can be fought only with heavy doses of herbicide. Burning is not an option because the leaves contain a highly flammable oil and the intense heat wipes out every other life form in the area. The tree emits millions of seeds during the fire that take root in the fire zone. The Brazilian pepper has completely covered two large areas in the middle of the Everglades. The only way to get rid of it is to bulldoze everything, scrape away the limestone bedrock and cart it away in trucks. Lygodium or Old World climbing fern, originally was sold in nurseries as a houseplant. The plant's spores can fly for miles in a windstorm. It has covered islands in the Everglades and has drifted west into the Loxahatchee National Wildlife Refuge, where it has proliferated during the last decade. An aerial survey in 1997 determined that 39,000 acres of South Florida were infested with lygodium; that number had increased to 100,000 acres by 1999. An Australian moth feeds on the fern, and biologists are studying the moth to determine if the cure will cause additional problems. Refuge managers attack lygodium with herbicide and machetes. Asian swamp eels, most probably dumped in canals in South Florida, could be heading for the Everglades, where they will eat shrimp and small fish and disrupt the food supply of migratory birds.
Postscript
The Missouri legislature is considering HB473 (co-sponsored by Robirds, Kreider, and Myers) to require persons, corporations, state, county and township agencies and boards as well as school boards, drainage boards and railroads to control the spread of kudzu and teasel.
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